A few things:
1) re bringing a gun: just to clarify a little more than just don't bring it, bringing a gun to Canada and not declaring it, or being pulled over while in Canada with it will result in an extended stay in one of our finer 1 star federal hotels with barred windows and doors.
2) Port Huron crossing is not too busy, Most of the Niagara crossings are usually very busy, Fort Erie is probably the least busy in the Niagara area.
3) the drive along the 402-401-403 Between Port Huron and Niagara is an easy drive with very little traffic
4) bringing food into Canada is the easy part, we shop in Port Huron all the time and have never had issues bringing it back. The hard part will be bringing food back to the USA. The rules are complex and seem to change daily. Rule of Thumb seems to be anything perishable is likely to be a problem going into the USA.